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Eocene Split
The Oligocene-Miocene boundary, about 23 million years ago, was one of the most drastic faunal turnovers of the Cenozoic era. During this time the world started to drastically cool as tropical forests gave way to grasslands and the once diverse Oligocene megafauna started to decline. Many well-known beasts from entelodonts to perissodactyls started to decline. This was a new age. The age of the pecorans; and the and the age of grass, and ice, feeding on the loss of the great Eocene forests, and with them all of their flora and fauna. Then the world started to become an icehouse. The ice caps started to develop. The ice age began. An unimportant primate from the African savannah became a skilled hunter and conquered the world. And it was driven by the savannahs where it evolved, a result of the sudden domination of the grasslands in the Miocene. But this timeline is different. Grass never fully diversified, inhibiting the development of the ruminants, with the Pecora, one of the most successful recent groups of mammals, on the brink of extinction. The split happened in the early Oligocene, meaning that more of the unfamiliar Eocene fauna was kept, and the Neogene fauna was almost nonexistent. The world stayed in greenhouse climate for the rest of the Cenozoic. And thus, an entire new Earth was created. History Note: These periods go by HE timeline, and do not reflect changes in the fauna and climate of this timeline. Geologic divisions are not necessarily different from HE in this scenario. Oligocene The point of divergence was 32 million years ago; although it can be located, it was not a drastic change from Home Earth. Unlike in other scenarios, which add or subtract extinctions, this timeline simply has a slightly hotter temperature, which led to grass becoming far less common than in our timeline. The first group to extinct was the Mesonychia, but this was no surprise considering that they were already in decline. We are assuming that all groups disappearing during the Eocene-Oligocene boundary did indeed go extinct, so such animals as Brontotheriidae and Multituberculata are not in this timeline. Although ambiguity exists on whether the Xiphodontidae did or did not go extinct during the Eocene-Oligocene extinction, they survived in this timeline, though not for long. The perissodactyls stayed in domination, and the tylopods did well. The Cetancodontamorpha (pan group Whippomorpha) were represented by the Anthracotheriidae; entelodonts; and the cetaceans, which started declining due to the Mysticeti and Odontoceti not taking over. Meanwhile, the Desmostylia (which evolved slightly earlier than shown in the fossil record) and Sirenia were doing well in the seas, but still kept some basal forms. All primate groups survived, with the exception of the sparse North American primates, which went extinct after being nearly decimated by the drastic climatic change of the Eocene-Oligocene boundary. The climate of the late Oligocene was warmer than in HE's Oligocene, but was the coldest and driest time period after the split. Still, the animals that survived the extinction were well-adapted, and the only groups going extinct during the period were "dead clades walking". Besides the Mesonychia, these included the Palaeotheriidae. The Eocene conditions were about to return, though, because the Earth was heading for a thermal maximum. Miocene The Miocene reverted to a warmer climate, and although most groups survived some were wiped out entirely. Rainforests quickly spread throughout the world, and Eocene temperatures returned. The Miocene Thermal Maximum occurred 15 Ma before present, and it's effects were quite surprising. The Xiphodontidae, always on the brink of extinction, quickly died out. Equidae was severly damaged, with only one species surviving. The Pyrotheria went extinct in South America, already on the decline and in competition with Astrapotheria, which had a nearly identical niche. Entelodonts, already in competition with so many other carnivores, were all wiped out except for an isolated pocket in the heart of North America, where the carnivorans and creodonts were few. But most dramatic of all, the cetaceans, the most aquatically adapted of all tetrapods of the time, went completely extinct. Several groups, such as the Ruminantia, which hadn't been competing with other ungulates; Creodonta, which held firm carnivorous niches; Tylopoda, which were major herbivores; and Perissodactyla, which also held a similar herbivorous niche were not affected by the extinction. But three groups thrived in the climate, and they were to dominate for the rest of the timeline. These were the primates, because of the forests they do so well in; the carnivorans, because they could grab niches from the entelodonts; and the crocodilians, which not only took over the niches of large carnivores on every continent, but also evolved an aquatic group which converged with the Thalattosuchia. Now, the niches were set for the rest of the timeline, and evolution could continue uninterrupted – well, with the exception of the rise of the now fierce crocodilians, and the resulting possible extinction of many mammalian carnivores. Pliocene After the Miocene Thermal Maximum, which brought the extinction of several groups, and the decline of many others, albeit helping at least three groups; the temperature began to cool again. By the early Pliocene, the temperatures were back to those of the time of the split. It was still a hothouse world, but not like the Miocene or Eocene. By the Pliocene, all groups had their modern niches, with only a few changes from after the Miocene Thermal Maximum. During this period, the main changes in niche were the spreading tylopods, especially the Anoplotheriidae; the increasing prominence of the Carnivora, namely the saber-toothed Nimravidae; and two crocodylomorph changes, which were the increase in sebecosuchian dominance in South America and the Neothalattosuchia, a group of sea monsters derived from usual crocodilians. Certain groups, mostly the Phorusrhacidae (actually because of sebecosuchian competition), decreased in diversity, but Equidae was heavily restricted. As for other reptiles, by this time, Crocodylomorpha was probably the most successful group of reptiles, and continued to be; but Squamata and Choristodera were doing well in the hot climate, which especially helped the Choristodera, which went extinct due to cold temperatures in our timeline. However, around the middle of the Pliocene, Sphenodontia went extinct, as they were already declining. Then, during the late Pliocene, the temperature began to rise again, perhaps due to increased volcanic activity. This was only a relatively minor fluctuation, though, and did not lead to any sort of thermal maximum. Quaternary The Quaternary was little more than an extension of the Pliocene in this timeline, with previous trends continuing. The anoplotheres continued to conquer territory, hopping islands and becoming possibly the only group to reach South America during the Cenozoic. With a higher sea level, the Isthmus of Panama never formed, and South America stayed as isolated as Australia, with their unique sparassodonts and xenarthrans. Although cooler than the late Pliocene, the Quaternary was no glaciation, or anything near a glaciation. A short temperature dip, lasting about 50,000 years, occurred during the mid-Pleistocene, about 1.5 million years ago. The creodonts started to decline, and the saber-toothed nimravids showed they had a clear advantage over almost all other mammalian carnivores. Although carnivorans encompassed everything from non-canine canids to bear dogs, the creodonts still held most niches not held by the carnivorans. Despite a carnivoran domination on most continents, South America few placentals, only xenarthrans, rodents, Meridiungulata, and Platyrrhini, with the carnivorans and creodonts being absent; and Africa was relatively conservative, with the creodonts doing very well here. As for primates, strange forms like adapids remained dominant, and the Sivaladapidae gave rise to the sivalads, which have the intelligence of apes. And there it is – what happened to the Earth in a timeline where a small fluctuation in temperature stopped the grasslands from dominating, and ultimately changed the course of evolution. Category:The Modern Oligocene Category:Alternative Evolution